Analysis of dynamics of vocal tract system using zero time windowing method

Abstract

Speech signal is the output of a dynamic production mechanism. The articulators involved in the production process move continuously at different rates, giving rise to a time varying vocal tract transfer function. The process of speech production is dictated by the linguistic and para linguistic information being conveyed by the speaker. Algorithmic processing of the speech signal attempts to study the behavior of the acoustic response of the vocal tract system during the production of different sounds. newline newlineThere are some involuntary or semi voluntary movements of articulators that take place due to factors such as the air pressure and muscular tension. Glottal opening and closing, and the velar opening and closing are two examples of such movements during the production of voiced and nasal sounds, respectively. Traditional methods to study the speech production mechanism assume stationarity of the vocal tract acoustic system over a short duration. These methods do not capture the continuous changes in the production system response with time. newline newlineThe objective of this study is to examine changes in the vocal tract system to bring out the dynamic nature of the system during production of different sounds. The glottal and velic activities result in coupling and decoupling of different tracts in production system. The present study utilizes a speech analysis method, called the zero time windowing (ZTW). The ZTW method gives spectral characteristics at each instant of time, reflecting the instantaneous behavior of the production system. The spectral characteristics are derived using the Hilbert envelope of the numerator of the group delay (HNGD) function. The time varying behavior of the system response is captured using the dominant resonance frequency (DRF) obtained from the HNGD spectrum. Changes in the production system during the glottal and velic activity is reflected as shift in the locations of the DRFs. The thesis further examines production system characteristics for nasal, approximant and fricative sounds